Based on 11‐year's period data of the sunspot and the periodic variation of the magnetic field of the sunspot, the time series of the magnetic index of the sunspot magnetic field (MI) is established. The analysis indicates that the average period of the solar magnetic activity is about 22.2 years, but it is not a constant. In most cases, when the period is short, the magnetic index is large, corresponding to strong solar activity; when the period is long the magnetic index is small, corresponding to weak solar activity. The time series of magnetic index of the sunspot magnetic field has also a period of 80~90 years. This study shows that during the period of MI curve rising from its minimum to maximum, the solar magnetic field is southward, and the planetary magnetic lines and the Earth magnetic lines meet together. The magnetic layer is an open layer, with the solar wind entering into the Earth magnetic layer from the sunny side taking plenty of plasma, increasing the input kinetic, heat and electromagnetic energy greatly, which corresponds to the temperature increasing period in the troposphere of the Northern Hemisphere. On the other hand, during the period of MI curve descending from the maximum to minimum, the solar magnetic field is northward, same as the top of the magnetic layer direction, and the planetary magnetic lines and the Earth magnetic lines do not meet. The magnetic layer is a close layer; only a few electriferous particles can enter the Earth magnetic layer through magnetic lines, corresponding to the temperature decreasing period in the troposphere of the Northern Hemisphere.